Keywords: soil nutrient balances, soil fertility degradation, East Africa , participatory innovation, experiential learning, farmer field schools, smallholder agriculture <br/> <br/> Maintaining and improving soil fertility is crucial for Africa to attain the Millennium Development Goals. Fertile soil and balanced soil nutrient management are major foundations for sustainable food production, contribute to a sound management of natural resources and assist in controlling environmental degradation such as erosion, loss of biodiversity, pollution of water sources and acidification. This thesis describes the development of an inter-disciplinary diagnostic tool to assess impacts of farm management practices on nutrient balances and the use of the tool in participative research and innovation approaches in East Africa over a ten-year period from 1995 to 2005. <br/> <br/> The structured conceptual framework and related NUTMON approach facilitate a comprehensive description and analysis of management practices in complex smallholder farming systems. The approach has been successfully applied in a variety of projects addressing soil fertility degradation in Africa and Asia . A wide audience from both the research and development communities have been exposed to the approach. The integration of biophysical, financial and livelihood aspects in the analyses proved essential to assist effective decision making by farm households. The quantitative analysis based on farmers’ own data and observations, complements other participative tools and contributed to learning and innovation processes within households. <br/> <br/> The various projects which implemented the approach showed that negative soil nutrient balances and high incidence of poverty prevail in most of the farming systems in East Africa . However, huge variations between geographical areas and individual farms were observed. Farmers often successfully integrated technical innovations in existing farm management systems, whereby combinations of application of organic manure and fertilizers appeared to be the most effective strategy. The research has shown that, once smallholders are equipped with knowledge and the capacity to learn, are empowered in organizations and connected to markets and the private sector, they can substantially improve their rural livelihoods. Therefore a focus on participatory experiential learning approaches and farmer organizations that result in new arrangements in innovation systems needs to be mainstreamed in rural development projects. Experiences show that the sustainability of group learning processes increases considerably when the groups engage successfully in commercial activities at the same time. <br/> Innovations in soil fertility management were most successful and had the greatest impact on livelihoods in areas with both high agricultural potential and access to large urban markets. Investments in soil management or other technologies can be realised more easily by smallholders when they have opportunities to generate cash through commercial sales and value-addition, or when they have access to non-farm income. In more marginal areas most investments in inputs and technologies were financially unattractive or risky. In these areas priority needs be given to creating a more conducive environment for smallholders to do business and explore alternatives to food crop production. <br/> <br/>